Overweight and obesity rates are increasing in children of preschool age. Little is known about the physical activity levels of children in preschools, but it is likely that decreasing physical activity is contributing to increased overweight and obesity. In addition, the influence of motor development status on physical activity in young children has not been fully explored. The proposed supplement study would extend an ongoing investigation, "Physical Activity in Preschool Children" (1R01 HD043125), which is examining the physical activity behaviors of children in the preschool setting using accelerometers and an observational system. The study is also identifying physical, social, and institutional factors that influence young children's physical activity behavior. The proposed supplement study would examine out-of-school and total physical activity of preschool children and would assess motor development status and its influence on physical activity behavior. The ongoing study is being conducted in 24 preschools. The proposed supplement study will be conducted in the same preschools; subjects will be 480 3-, 4-, and 5-year-old children. Children will wear an accelerometer during out-of-school hours on five school days and one weekend. Their motor development status will be assessed using The Test of Gross Motor Development, Second Edition. A cross-sectional, observational study design will be used. To describe associations between out-of-school and total moderate-to-vigorous physical activity (MVPA) and the factors that are hypothesized to influence MVPA, including motor development status, a series of mixed model analyses will be performed. These analyses will include preschool as a random effect to account for the intact social grouping of children within preschools. Also, multivariate analyses including both individual and school-level independent variables will be performed. The proposed supplement study will extend the effectiveness and efficiency of the ongoing study in addressing a critical public health problem, the increasing prevalence of overweight and obesity in children, and will establish a foundation for future intervention studies and for the development of effective health policies. [unreadable] [unreadable]